Plants- ap bio?

Question

how plants colonized and transformed Earth. what's a seed plant and why are humans so dependent on these plants?

Answer 1

the strictly modern sense, the name plant refers to the biological classification kingdom Plantae. However, other photosynthetic organisms, including protists, green algae, and cyanobacteria have evolutionary significance to modern plants. While this article is directly about the evolutionary history of the Plant kingdom, these other organisms provide clues to the evolution of all photosynthetic organisms. All of these organisms, plants, green algae, and the protists, are primary photosynthetic eukaryotic organisms.

Scientists start the search for fossil evidence of plants with indirect evidence for their presence, the evidence of photosynthesis in the geological record. The evidence for photosynthesis in the rock record is varied, but primary evidence comes from around 3000 Ma, in rock records and fossil evidence of cyanobacteria, a photosynthesizing prokaryotic organism. Cyanobacteria use water as a reducing agent, thereby producing atmospheric oxygen as a waste product, and profoundly changing the early reducing atmosphere of the earth to one in which modern aerobic organisms eventually evolved. This oxygen liberated by the cyanobacteria then oxidized dissolved iron in the oceans, the iron precipitated out of the sea water, and fell to the ocean floor to form sedimentary layers of oxidized iron called Banded Iron Formations (BIFs). These BIFs are part of the geological record of evidence for the evolutionary history of plants by identifying when photosynthesis originated. This also provides deep time constraints upon when enough oxygen could have been available in the atmosphere to create the ultraviolet blocking stratospheric ozone layer. The oxygen concentration in the ancient atmosphere subsequently rose, acting as a poison for anaerobic organisms, and creating a highly oxidizing atmosphere with niches on land for aerobic organisms.

Evidence for the cyanobacteria also comes from the presence of stromatolites in the fossil record deep into the Precambrian. Stromatolites are layered structures that were (and still are today) formed by the trapping, binding, and cementation of sedimentary grains by microorganisms, such as cyanobacteria. The direct evidence for cyanobacteria is less certain than the evidence for their presence as primary producers of atmospheric oxygen.

Chloroplasts in eukaryotic plants evolved from an endosymbiotic relationship between a cyanobacterium and a non-photosynthetic eukaryotic organism, creating a lineage that eventually led to photosynthesizing eukaryotic organisms in marine and freshwater environments. These earliest photosynthesizing single-celled algae eventually evolved into larger multicellular photosynthetic organisms such as the Chlorophyta and later the Charophyta, fresh-water green algae, which are thought to contain the ancestors of land plants.

Answer 2

According to geologic studies and the theory of evolution, the appearance of land plants that perform photosynthesis are the reason why other animals were able to move to land and live.  Remember that plants perform photosynthesis and as a result release oxygen into the atmosphere.  Before land plants, oxygen molecules were bound to other molecules such as CO2 and H2O, there weren't any free oxygen molecules to breath.  Plants provided this.  

Plants themselves have the ability to spread and reproduce very rapidly, allowing them to quickly colonize and populate areas simply because they are only dependent on the sun, water and abundant CO2 already in the atmosphere.  

A seed plant is any plant that reproduces with seeds, which are the vast majority of plants.  The seeds, once given the right conditions and elements such as nitrogen and phosphorous from the soil as well as water and some sun begin to grow and photosynthesize.  As a result, they too will produce more seeds and further populate the area.  

Humans are dependent on plants in general for two main reasons.  First, plants are the producers in any food chain.  Anything we consume as food has a direct or indirect relationship with plants.  Glucose, another product of photosynthesis, is found in virtually every food in some amounts and is essential for healthy brain function.  It is thought that as the human diet improved and moved from simple hunting and moved to actually consuming and cultivating plants, glucose provided the nutrients necessary for our brains to evolve.  Second, plants provide the oxygen we breathe.  Without plants, our bodies cannot get enough oxygen to allow our bodies and cells to respire (breathe).  

Seed plants are especially beneficial because they allow a way for humans to gather a form of the plant for use in farming or as a personal food source.  Humans cannot make more plants without their seeds.  These seeds, in a way, are the foundation for our food sources on this planet today.